In general, magnetic resonance imaging (MRI) examinations are based on the interactions among a primary magnetic field, a radiofrequency (RF) magnetic field, and time varying magnetic gradient fields with gyromagnetic material having nuclear spins within a subject of interest, such as a patient. Certain gyromagnetic materials, such as hydrogen nuclei in water molecules, have characteristic behaviors in response to external magnetic fields. The precession of spins of these nuclei can be influenced by manipulation of the fields to produce RF signals that can be detected, processed, and used to reconstruct a useful image.
Techniques have been developed to perform MRI imaging sequences to generate diffusion information that might be indicative of tissue microstructure, and/or to evaluate tissue for various abnormalities, such as neural injuries, neural degenerative disorders, and so on. In diffusion imaging, information is encoded in both image space and diffusion space, the latter typically referred to in the art as q-space. Typically, q-space is utilized to detect the movement of hydrogen nuclei in water molecules. Diffusion encoding gradient pulses are utilized to characterize the three-dimensional movement of the water molecules within and between tissues—more specifically within individual voxels (each spatial location). The movement of the water molecules may be characterized as incoherent motion, which results from diffusion processes, and coherent motion, which results from tissue movement, such as during pulsation.
The data that is obtained from q-space acquisitions may be categorized into either diffusion spectrum imaging (DSI), single-shell acquisition (e.g., high-angular diffusion imaging (HARDI)), or multi-shell acquisitions, depending on the sampling technique. However, due to the high dimensionality of the acquisition techniques (e.g., 3D in spatial domain and 3D in q-space), evaluating the diffusion properties of water in vivo may result in extended scan times to acquire acceptable data for image reconstruction.